The invention relates to an airbag module for motor vehicle steering wheels, having a gas generator, a folded together airbag, a dish-like generator support, a covering which is connected to the generator support at the edges that has predetermined breaking points and also having a retaining plate for fastening the airbag on the generator support, all the elements mentioned forming a one-part structural unit which can be connected to a steering wheel.
Such modules are nowadays fitted as standard into virtually all passenger cars and must therefore be designed for mass production. This includes the requirement that, as far as possible, they are to be suitable for use not only for one type of vehicle or steering wheel but be of a size suitable for fitting a number of types, in order that the advantages of high production numbers can be fully utilized. The outer dimensions of the module must in this case be chosen such that the largest gas generators and airbags which may exist within the application range of the modules can be accommodated in said module. This provides one determinative boundary condition for the design of airbag modules.
An entirely different boundary condition arises from the fact that the covering must of course be provided with predetermined breaking points in such a way that the airbag can unfold rapidly and unhindered in the case of its use. On the other hand, the predetermined breaking points must not be weakened, or even break unintentionally, during the at least ten years of use of the motor vehicle. For the compromises which have to made in this connection there have already been made numerous proposals which have also proved successful in practice, because the airbag folded together underneath the covering generally serves as an abutment, with the result that the covering cannot be pressed inward to the extent that an overloading of the predetermined breaking point could occur when the steering wheel is handled in the customary way. For this purpose, the folded together airbag must entirely fill the volume available.
This precondition is no longer met, if, for example, a new gas generator of a smaller overall volume is to be used, if a novel fabric for the airbag takes up less volume or if in mass production it is intended to use airbag modules of predetermined outer dimensions such that the volume required for the gas generator and the folded together airbag is too large. In these cases, there is no abutment for the covering and, under certain circumstances, the predetermined breaking points experience excessive loading, which during normal use of the steering wheel could lead to unintentional breakage and make repair work necessary, in most cases substitution of the entire airbag module being the only option because individual covers are either not readily available on the market or else cannot be fitted with the means available in a workshop.